On Wednesday, Apple released its long-awaited OS X Mountain Lion upgrade through the Mac App Store. The download is 4.05GB, and retails for US$20.

The software incorporates a number of apps previously exclusive to iOS, including Notes, Reminders, Game Center, and the Notification Center. It also more deeply integrates iCloud, and introduces Gatekeeper, a new security system designed to prevent malware from being installed. In all, Apple claims that over 200 new features have been added including the following:

Messages:
- Send messages from your Mac to friends with an iPhone, iPad, or Mac.

- With iMessage, you can start a conversation on your Mac and pick it up on your iPhone or iPad.

- Power Nap keeps your Mac up to date while it sleeps so it’s instantly ready to go.

- Gatekeeper makes it safer to download apps from the Internet by giving you control over which apps can be installed on your Mac.

- New features for Chinese users include improved text input, leading search engine Baidu as an option in Safari, sharing to microblogging service Sina Weibo and video websites Youku and Tudou, eight new fonts, and a new Chinese dictionary.